Stonemasonry Rule Number 1 Do not mix iron, cement and and limestone.

Wipe with damp cloth or mist with water to oxidise iron filings.

In the knowledge that one should never combine cement and iron with natural stone I thought it would be fun to do exactly that.

Used salvaged stone, cut to size, scribed on portal, cut out slot with angle grinder, mixed neat cement with water and iron filings, estimating quantities, left 24 hours to set, cut off face, dried. Nervous then exhilarated.